The present invention relates to a process and system for quickly locating coated cooling holes in a part, such as a turbine vane, even though such holes are only partially visible. In a first embodiment of the present invention, the process and the system for locating the coated cooling holes uses thermal imaging techniques to determine the position of the cooling holes. In a second embodiment of the present invention, the process and the system for locating the coated cooling holes uses laser scanning techniques to determine the position and orientation of the cooling holes.
Currently, the repair process for turbine vanes involves cleaning the vanes and applying turbofix, a putty-like substance, over the entire vane area to cover the cooling holes and any cracked areas. The vanes are then brazed and the excess turbofix is removed by manual blending. The refurbished vanes are coated with a thermal barrier coating (TBC) and laser drilled to re-install the cooling holes.
In many cases, only a small section of the vanes need to be turbofixed and blended because the rest of the vane sections are good and do not need any additional operations other than the re-application of the thermal barrier coating. The re-application of the thermal barrier coating blocks the existing cooling holes. In these cases, if it were possible to locate the cooling holes, even though they are only partially visible, then the thermal barrier coating from the cooling holes can be removed by laser reaming. If used on turbine vanes, this process will save time and labor in the turbofixing, blending and laser drilling operations as only the necessary sections are turbofixed and blended. It is difficult to turbofix some vanes due to the geometry of the vanes and in these cases, locating the cooling holes to remove the thermal barrier coating becomes critical.
Since there is no current process available to locate the cooling holes precisely, all the vanes are fully turbofixed in many cases, even those not needing full treatment. If the holes could be located through the coating, then a lot of the turbofixing and blending can be eliminated with a drastic reduction in process time and turnaround time.
The problems in locating the TBC coated cooling holes are many. The first and the most challenging part is that the holes are partially covered by the thermal barrier coating, hidden to various extents, by the coating process. The second is that the cooling holes are very small, around 0.020 inches in diameter, and they need to be located precisely on a complex airfoil shape that is distorted to various extents during its operational life on the engine.
The present method for locating the position of a given cooling hole is manually locating each hole individually by viewing through a lens system and then laser reaming it. This method is time consuming and not accurate since the holes are only partially visible at best. The method involves a great deal of operator guesswork.